Windows server 2003 hardware requirements are stated below. Please note these are the minimum requirements for a stable windows server 2003.

Requirement Standard Edition Enterprise Edition Datacenter Edition Web Edition
Minimum CPU Speed 133 MHz 133 MHz for x86-based computers733 MHz for Itanium-based computers* 400 MHz for x86-based computers733 MHz for Itanium-based computers* 133 MHz
Recommended CPU Speed 550 MHz 733 MHz 733 MHz 550 MHz
Minimum RAM 128 MB 128 MB 512 MB 128 MB
Recommended Minimum RAM 256 MB 256 MB 1 GB 256 MB
Maximum RAM 4 GB 32 GB for x86-based computers512 GB for Itanium-based computers* 64 GB for x86-based computers512 GB for Itanium-based computers* 2 GB
Multiprocessor Support ** Up to 4 Up to 8 Minimum 8 requiredMaximum 64 Up to 2
Disk Space for Setup 1.5 GB 1.5 GB for x86-based computers2.0 GB for Itanium-based computers* 1.5 GB for x86-based computers2.0 GB for Itanium-based computers* 1.5 GB

I believe, a good beefy hardware configuration with 1.0 GHz, 512 MB RAM with Hard Drive of 20GB. for a computer running Windows Server 2003 is a processor in excess of 900MHz, with 512MB of RAM and three 20 GBSCSI drives .